The present invention relates to a method and a device or apparatus for carefully adjusting the tolerances of an article made from vibrated concrete in a mold after removal of the article from the mold. The adjusting refers both to dimensions and shape of the article.
When making articles from concrete which must have a high degree of precision, both regarding dimensions and shape, it has been common practice to use a rather dry concrete composition and to stamp or press it in a mold before removing the article therefrom and letting the concrete harden. Though making possible very close tolerances, both regarding dimensions and shape, such a method of manufacture has the drawback that the concrete, due to its low water content, does not have satisfactory strength.
In such cases where the method of manufacture indicated above has not offered a strength high enough, there has up to now not existed any technique useful in practice for making concrete articles with very close tolerances regarding both dimensions and shape. This is due to the fact that concrete having the proportions of its ingredients optimized as regards strength cannot be pressed to form a rigid body in the manner indicated above but instead, to achieve maximum strength, must be vibrated so that the density is increased as much as possible. Even after vibrating, concrete of this composition is rather easily deformable, with the results that such an article removed from the mold can be deformed under influence of gravity, and further that removal from the mold proper often creates difficult problems by causing different kinds of deformation or damage to the article. This is due to the fact that concrete of this quality has a very troublesome tendency of adhering to the surfaces of the mold so that the removal itself often causes strong suction forces to the concrete articles, thereby causing deformation or damage.